Non-linear relationship between chromatin accessibility and estradiol-regulated gene expression

Chromatin accessibility is central to basal and inducible gene expression. Through ATAC-seq experiments in Estrogen Receptor-positive (ER+) breast cancer cell line MCF-7 and integrationvwith multi-omics data, we found that estradiol (E2) induced chromatin accessibility changes in the widely studied E2-regulated genes. As expected, open chromatin regions associated with E2-inducible gene expression showed enrichment of estrogen response element and those associated with E2-repressible gene expression were enriched for PBX1, PBX3, and ERE. Surprisingly, a significant number of E2-inducible genes displayed closed promoters/enhancers and these were enriched for binding for transcription factors such as NF-Y, FOXA1, GRHL2, and BATF, which are known to interact with nucleosomes. While a significant number of open chromatin regions showed FOXA1 occupancy in the absence of E2, E2-treatment further enhanced FOXA1 occupancy suggesting that ER-E2 enhances chromatin occupancy of FOXA1 to a subset of E2-regulated genes. In summation, our results reveal complex mechanisms of ER-E2 interaction with nucleosomes. We conducted both ATAC-seq and RNA-seq for MCF7 cells. Total RNA from MCF-7 cells treated with vehicle ethanol or E2 for three hours in biologic triplicates was used for sequencing. MCF-7 cells treated with vehicle (ethanol) control, E2 (10-10 M) for one or three hours were were done in biologic triplicates with ~50,000 cells.